1. Technical Field
The invention relates to suspension systems for vehicles, such as trailers and trucks. More particularly, the invention relates to a suspension assembly having a torsion axle in combination with an air spring. Even more particularly, the invention relates to a more compact, lighter weight combination torsion axle-air spring suspension assembly than known prior art combination suspension assemblies.
2. Background Information
Torsion axles have been known for many years, such as shown in U.S. Pat. No. 2,998,981. Torsion axles have proven to be extremely popular because if one wheel hits a bump or rut, it can react independently of the other wheel, which may not hit a bump or rut at the same time. This torsion axle concept operates to keep a trailer moving as straight as possible behind a towing vehicle and absorbs some of the shock of the road over which it is passing with an independent suspension. This is contrasted with a straight axle where if one wheel drops into a rut or is slowed down for any reason while the other wheel of the trailer does not have the same experience at the same time, the trailer would tend to turn somewhat to allow the wheel that is on the flat part of the road to move forward while the wheel that is in the rut is restrained, therefore causing the axle not to be perpendicular with the direction of towing of the vehicle itself.
Most torsion axles are constructed of a square axle in cross section with elongated rubber members disposed in-between the square axle and a larger outer tube. U.S. Pat. Nos. 5,161,814 and 5,820,156 disclose such a construction. One common torsion axle is a TorFlex® rubber torsion suspension system distributed by Dexter Axle. This type of torsion axle has independent and separate stub axles or stub shafts on each end which are part of spaced suspension assemblies mounting each of the wheels on the trailer frame to enhance the independent aspect of such an axle.
Torsion axles can also be constructed as in U.S. Pat. No. 5,163,701 which uses a plurality of elongated bars which can twist and bend but return to their original position after such bending. It is also known to use air bags, commonly referred to as air springs, for straight, non-torsion axles, such as shown in U.S. Pat. Nos. 3,784,221 and 5,427,404. While it is true that both the torsion axle technology and the air spring technology has been quite successful independently in making a smoother ride and enhanced the handling performances of vehicles having such suspension systems, these suspension systems still have their shortcomings and there is a need for improvement thereto.
The vehicle suspension system of U.S. Pat. No. 6,340,165 combines the advantage of both the torsion axle and air spring into a single suspension assembly and has provided a more efficient and better performing suspension system than that believed provided by the systems using only a torsion axle or only an air spring.
The suspension assembly of the present invention improves on the system of U.S. Pat. No. 6,340,165 by providing a more rugged, compact, lighter weight structure by shortening the distance from the pivot axis of the air spring support arm to the axis of the torsion axle and to the centerline of the air spring. This results in lower torque on the axle tube in roll or diagonal walk or tramp. This lower beam stress enables lighter, less expensive beams and axle connections to be utilized. It provides less vertical axle tube motion and enables lower design heights to be achieved. The air spring of the present invention nests behind the axle tube and generally inboard of the swing arm, and provides better ground clearance particularly in rebound.